Patterning nano-scale patterns on a film comprising unzipping copolymers

ABSTRACT

The invention concerns a method for patterning a surface of a material. A substrate having a polymer film thereon is provided. The polymer is a selectively reactive polymer (e.g., thermodynamically unstable): it is able to unzip upon suitable stimulation. A probe is used to create patterns on the film. During the patterning, the film is locally stimulated for unzipping polymer chains. Hence, a basic idea is to provide a stimulus to the polymeric material, which in turn spontaneously decomposes e.g., into volatile constituents. For example, the film is thermally stimulated in order to break a single bond in a polymer chain, which is sufficient to trigger the decomposition of the entire polymer chain.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/894,412, filed Sep. 30, 2010, the disclosure of which is incorporatedby reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to the field of probe-based methods for patterninga surface of a material, such as scanning probe lithography (hereinafter SPL). In particular, it may be directed to high resolutionpatterning on a surface of a material, such as nano-scale patterns withfeature sizes of e.g., less than 32 nanometers (nm).

BACKGROUND OF THE INVENTION

Lithography is a process for producing patterns of two dimensionalshapes, consisting of drawing primitives such as lines and pixels withina layer of material, such as, for example, a resist coated on asemiconductor device. Conventional photolithography (also called opticallithography) is running into problems as the feature size is reduced,e.g., below 45 nm. These problems arise from fundamental issues such assources for the low wavelength of light, photoresist collapse, lenssystem quality for low wavelength light and masks cost. To overcomethese issues, alternative approaches are required.

Examples of such alternative approaches are known in the field of theso-called nanolithography, which can be seen as high resolutionpatterning of surfaces. Nanolithography refers to fabrication techniquesof nanometer-scale structures, comprising patterns having one dimensiontypically sizing up to about 100 nm (hence partly overlapping withphotolithography). Beyond the conventional photolithography, theyfurther include such techniques as charged-particle lithography (ion- orelectron-beams), nanoimprint lithography and its variants, and SPL (forpatterning at the nanometer-scale). SPL is for instance described indetail in Chemical Reviews, 1997, Volume 97 pages 1195 to 1230,“Nanometer-scale Surface Modification Using the Scanning Probemicroscope: Progress since 1991”, Nyffenegger et al. and the referencescited therein, see also Garcia, R.; Martinez, R. V. & Martinez, J.,Nano-chemistry and scanning probe nanolithographies, Chem. Soc. Rev.,Royal Society of Chemistry, 2006, 35, 29-38.

In general, SPL is used to describe lithographic methods wherein a probetip is moved across a surface to form a pattern. Scanning probelithography makes use of scanning probe microscopy (SPM) techniques. SPMtechniques rely on scanning a probe, e.g., a sharp tip, in closeproximity with a sample surface whilst controlling interactions betweenthe probe and the surface. A confirming image of the sample surface canafterwards be obtained, typically using the same scanning probe in araster scan of the sample. In the raster scan the probe-surfaceinteraction is recorded as a function of position and images areproduced as a two-dimensional grid of data points.

The lateral resolution achieved with SPM varies with the underlyingtechnique: atomic resolution can be achieved in some cases. Use can bemade of piezoelectric actuators to execute scanning motions with aprecision and accuracy, at any desired length scale up to better thanthe atomic scale. The two main types of SPM are the scanning tunnelingmicroscopy (STM) and the atomic force microscopy (AFM). In thefollowing, acronyms STM/AFM may refer to either the microscopy techniqueor to the microscope itself.

In particular, the AFM is a device in which the topography of a sampleis modified or sensed by a probe mounted on the end of a cantilever. Asthe sample is scanned, interactions between the probe and the samplesurface cause pivotal deflection of the cantilever. The topography ofthe sample may thus be determined by detecting this deflection of theprobe. Yet, by controlling the deflection of the cantilever or thephysical properties of the probe, the surface topography may be modifiedto produce a pattern on the sample.

Following this idea, in a SPL device, a probe is raster scanned across afunctional surface and brought to locally interact with the functionalmaterial. By this interaction, material on the surface is removed orchanged. In this respect, one may distinguish amongst:

-   -   constructive probe lithography, where patterning is carried out        by transferring chemical species to the surface; and    -   destructive probe lithography, which consists of physically        and/or chemically deforming a substrate's surface by providing        energy (mechanical, thermal, photonic, ionic, electronic, X-ray,        etc.).

SPL is accordingly a suitable technique for nanolithography.

High resolution patterning of surfaces is relevant to several areas oftechnology, such as alternatives to optical lithography, patterning forrapid prototyping, direct functionalization of surfaces, mask productionfor optical and imprint lithography, and data storage.

In particular, lithography can be used for the fabrication ofmicroelectronic devices. In this case, next to conventional lithography,electron-beam (or e-beam) and probe-based lithography are mostly in use.

For high resolution optical mask and nano-imprint master fabrication,e-beam lithography is nowadays a standard technology. However, whenapproaching high resolutions, writing times for e-beam mask/masterfabrication increase unfavorably.

As a possible alternative, the use of probes for such patterning isstill under development. At high resolution (<32 nm), the speed ofsingle e-beam and single probe structuring converges.

In the case of data storage, various approaches have been proposed tomake use of probes for storage in the archival regime. However, a mainchallenge that remains is to achieve long bit-retention. Usingthermomechanical indentation allows for instance to achieve satisfactoryendurance and retention of data. A thermomechanical approach, however,produces indentations that are inherently under mechanical stress.Therefore it is difficult to obtain retention times in excess of tenyears, as usually needed in the archival domain.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a method forpatterning a material, comprising: providing a material having a polymerfilm, the polymer film comprising polymer chains of copolymers derivedfrom two or more monomers, one of the monomers being a dialdehydecompound, whereby the polymer chains are able to unzip upon stimulation;and patterning the film with a nano-scale dimensioned probe, bystimulating the film for triggering an unzipping reaction of polymerchains of the film.

In other embodiments, the method may comprise one or more of thefollowing features:

-   -   the polymer film provided comprises polymer chains for which an        energetic or chemical modification event triggers the unzipping        reaction and wherein patterning includes stimulating the film        such that an energetic or chemical modification event occurs in        at least one polymer chain;    -   the polymer film provided comprises polymer chains which are        able to unzip upon breaking one chemical bond thereof and        wherein patterning includes stimulating the film to break one        bond of at least one polymer chain;    -   patterning includes having the probe provide an energy to the        film to activate a chemical reaction involving a reactant in        proximity with polymer chains, the chemical reaction allowing in        turn for unzipping at least one polymer chain;    -   the reactant is an acid-generator;    -   the polymer film is provided with the acid-generator comprised        therein, the acid-generator being activated during patterning;    -   the acid-generator is dispensed by the probe during patterning;    -   the acid-generator is a thermal-acid-generator, the        thermal-acid-generator activated by the probe, heated during        patterning;    -   the acid-generator is a photo-acid-generator, the        photo-acid-generator activated by light during patterning;    -   said one of the monomers is a phthalaldehyde compound;    -   polymer chains of the polymer film provided comprises copolymers        of phthalaldehyde compounds and benzaldehyde compounds;    -   at least some of the benzaldehyde compounds in the polymer        chains of the polymer film provided are functionalized        benzaldehyde compounds;    -   the polymer chains of the polymer film provided globally derive        from at least two compounds, one of the compounds being the        dialdehyde compound, and at least some of the polymer chains of        the polymer film provided comprise block copolymers of two or        more homopolymer units, one of the homopolymer units deriving        from the dialdehyde compound, whereby said at least some of the        polymer chains are able to unzip upon stimulation;    -   said at least some of the polymer chains of the polymer film        provided are ordered by way of another one of the homopolymer        units, substantially more stable than said one of the        homopolymer units upon stimulation;    -   the polymer chains in the polymer film provided have an average        orientation with a non-zero component perpendicular to a plane        of the polymer film;    -   the polymer chains in the polymer film provided are further        ordered such that said at least some of the polymer chains that        comprise block copolymers form a structured pattern in the plane        of the polymer film;    -   the polymer chains in the polymer film provided are further        ordered such that said at least some of the polymer chains that        comprise block copolymers form a two-dimensional lattice in the        plane of the polymer film; and    -   said one of the homopolymer units derives from a phthalaldehyde        compound, whereas another one of the homopolymer units derives        from a compound comprising a functional group capable of        initiating a ring-closing polymerization of phthalaldehyde.

The invention can further be embodied, in another aspect, as a materialcomprising a polymer film, the film comprising: polymer chains which canbe unzipped upon stimulation; and nano-scale dimensioned patterns in thefilm, the patterns obtained according to the invention.

According to yet another aspect, the present invention is embodied as amethod of reading nano-scale dimensioned patterns in a polymer film of amaterial, comprising: providing a material according to the invention;and reading the patterns.

Methods and materials embodying the present invention will now bedescribed, by way of non-limiting examples, and in reference to theaccompanying drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1-5 illustrate steps according to various embodiments of themethod of the invention;

FIG. 6A exemplifies selective removal of unzip polymer in an orderedblock copolymer film, in embodiments;

FIG. 6B illustrates in a perspective view the selective removal ofmicrodomains of unzip polymer in an ordered block copolymer film, inembodiments;

FIG. 7 depicts the chemical structure of a poly(phthalaldehyde), thatcan be used as one of the block of a copolymer, in embodiments;

FIG. 8 is an example of polystyrene-phthalaldehyde block copolymersynthesis, as used in embodiments;

FIG. 9 is an example of poly-L-lactide -phthalaldehyde block copolymersynthesis, as used in embodiments

FIG. 10 represents accessible functionalities for benzaldehyde compound;and

FIG. 11 is a possible reaction scheme for the co-polymerization ofphthalaldehyde and benzaldehyde monomers, as used in embodiments.

DETAILED DESCRIPTION OF THE INVENTION

As an introduction to the following description, general aspects of theinvention focus on a method for patterning a surface of a material. Amaterial having a polymer film thereon is provided. The polymercomprises chains which are able to unzip upon suitable stimulation(energetic or chemical modification event, protonation, etc.).Typically, the polymer is chosen such that stimulating a first chemicalmodification or degradation event triggers an unzipping effect, partialor total. To that aim, polymer chains of copolymers are derived from twoor more monomers, one of the monomers being a dialdehyde compound, e.g.,phthalaldehyde, which enables an unzip reaction upon suitablestimulation. A probe is then used to create patterns on the film. Duringthe patterning, the film is locally stimulated for triggering anunzipping reaction of polymer chains. As the unzipping effect isself-sustained, depolymerization is facilitated. Patterning a surface isaccordingly made easier compared to prior art methods. Deep patterns caneven be written with virtually no indentation force being applied to theprobe tip. This minimizes pattern distortion resulting from indenting ordisplacing the material. An advantage is that no fine-tuning ofintermolecular forces is required, at variance with materials requiringstabilization from secondary structure such as hydrogen bonds. Forexample, some of the polymer films as contemplated herein are notsusceptible to water and solvent uptake, which may result indeteriorating the patterning properties. A variety of methods canfurthermore be implemented for the activation of the intentionaldecomposition of such materials. For example, they can be thermallyactivated directly by the probe (energetic modification event).Alternatively, a chemical stimulus, e.g., a free proton from an acidgenerator included in the polymeric network, may serve this purpose.Finally, the copolymer chains involve at least another compound,distinct from the polyaldehyde, which is used to confer specificproperties to the film. For example, this other compound is chosen suchas to allow for easier functionalization than the polyaldehyde. In avariant, the polymer chains are synthesized into block-copolymers, oneof the block (polyaldehyde) enabling the unzip reaction, whereas theother one is used to order the block copolymer chains.

More details shall be given now, in reference to the figures.

FIG. 1 illustrates steps of the method according to a first embodimentof the invention. In reference to FIG. 1, a material 10, 20 is provided,having a polymer film 20 on a substrate 10, where the film comprises thepolymer chains 30. In FIG. 1, only one such chain 30 is depicted, forclarity. More will be said later about suitable polymers and how toobtain them.

The probe 50 is typically a SPM (e.g., AFM) probe mounted on the end ofa cantilever. The probe may thus be part of an AFM device (not shown),comprising electronic circuitry suitably designed to measure andcontrol, in operation, an interaction between the probe 50 and a samplesurface 20.

Engineering solutions, which are known per se, may further be providedsuch that it is possible to accurately control the relative position ofthe probe and surface, and possibly to ensure good vibrational isolationof the SPM. This can for instance be achieved using sensitivepiezoelectric positioning devices, as known in the art. Both verticaland horizontal controls of the probe are thus typically providedtogether with the SPM.

In a usual SPM device, the probe 50 is raster scanned above the samplesurface, such that imaging of the surface topology can be carried out.Here, the probe is rather used primarily to engrave patterns on thesurface of the film 20.

How the surface is patterned can be decomposed into several substeps.

Before patterning occurs properly, the probe 50 is maintained in a“non-patterning position”, that is, close to the surface of the film 20(not depicted). The probe is not yet in close enough contact to enablesurface patterning.

In the embodiment of FIG. 1, a first substep 110 consists of stimulatingthe film 20 e.g., directly with the probe. Here an energy sufficient forthe polymer to unzip is provided to the film, via an energeticmodification event, for example by raising the temperature of the tip inorder to provide thermal energy to the polymer resist. In particular,the polymer can be chosen such that the energy provided suffices tobreak one bond of one or more polymer chains 30, as depicted in FIG. 1,step 110. In practice, the probe is put in close proximity to or indirect contact with the surface of the film 20 while being suitablyheated. The force and the time of the exposure are tuned according tothe polymer used in the film and the desired patterns.

At least some of the polymer chains are able to unzip upon suitablestimulation, e.g., via an energetic or a chemical modification event.Such an event may for instance result in breaking a single chemical bondof the chain, which in turn triggers the unzipping reaction. Thiscontrasts with polymers (e.g., polystyrene, poly-α-styrene) which wouldunzip if the polymer chain has enough thermal energy to decompose. Here,one broken bond suffices to trigger the unzipping effect. As notedearlier, the latter is self-sustained, such that less energy needs to beprovided for the polymer to unzip during the patterning process.

The above principles are illustrated in steps 120 and 130 of FIG. 1. Atstep 120, degradation of a given polymer chain 30′ begins. At step 130,the polymer chain 30″ is entirely degraded, e.g., into volatiles such asmonomers. In other words, the polymer chain that was previouslystimulated (step 110) has now disappeared. A clean patterned surface isaccordingly obtained.

Briefly, a polymer chain part suitable to implement the above principleis a poly(phthalaldehyde), whose chemical structure is depicted in FIG.7. The present embodiment (i.e., FIG. 1) was notably implemented withpolymer chains comprising blocks of poly(phthalaldehyde) having amolecular weight of approximately 27 kDa, corresponding to ˜200 monomerunits per block (e.g., a typical monomer weight is 134). As the obtainedpolymer is thermodynamically unstable at room temperature, the energeticcost of the patterning process is very much affordable. More shall besaid in reference to FIGS. 7-11 below.

FIG. 2 is directed to another embodiment of the method according to theinvention. This embodiment is similar to FIG. 1, except that the probenow stimulates the film (step 220) with an energy adapted to activate achemical reaction 40′. Briefly, the chemical reaction involves areactant 40, 40′ in proximity with the polymer chains 30, whereby achemical modification of one polymer chain likely occurs. This shall inturn allow for unzipping polymer chains 30, 30′, 30″. The chain ofcausation is then interpreted as follows: a chemical reaction occurs;the chemical reaction triggers a chemical modification event (e.g., adegradation event) in a polymer chain; and the said event triggers theunzipping reaction. Hence, advantage is taken from the reaction toprovide the energy necessary for triggering and possibly maintaining theunzip effect. However, the principle remains the same as in theembodiment of FIG. 1: the film is stimulated such that an unzippingreaction is triggered. Accordingly, less energy is needed to pattern thefilm.

For example, the reactant can be an acid-generator. Preferably, thepolymer film 20 is provided with the acid-generator 40 comprised therein(e.g., immersed). Thus, the acid generator can be activated directly bythe probe 50 or by a light pulse at the level of the probe whenpatterning. Here, the depolymerization reaction is induced byprotonation, i.e., by the protons released upon activating theacid-generators immersed in the polymer melt. In other words, a chemicalreaction relays and even amplifies an initial energy stimulus, to allowfor the polymer chains to unzip.

The acid-generator may for instance be a thermal-acid-generator (TAG).The TAG molecules are thermally activated, e.g., by heating the probe asdescribed in relation to FIG. 1. In this case, the probe 50 is heated,step 220, FIG. 2, in order to activate the TAG 40′. The result issubstantially the same as what is obtained within the embodiment ofFIG. 1. In a variant, the TAG molecules could also be activated byheating the entire sample. In another variant, an electrical stimuluscould be used, relayed by the probe itself. Specific molecules known assquaric acid derivatives are particularly well suited to function asTAG.

In the embodiment of FIG. 3, the acid-generator is aphoto-acid-generator (PAG). In this case, the PAG is activated by light(e.g., by exposition to a light pulse 60), step 320, FIG. 3, in order toactivate the PAG 40′. The light pulse may be provided by a sourceexternal to the probe 50. In a variant, the PAG molecules are activatedby using the probe tip as a localized light source, as known fromnear-field-optical microscopy. The probe can be additionally heated inorder to assist the activation of the PAG molecules and thedepolymerization of the polymer chains.

In further embodiments (FIGS. 4 and 5), the probe itself acts as adispenser tool. Protons can for instance be provided in a native statein an acidic solution or in the form of TAG molecules dissolved in asuitable solvent, FIGS. 4 and 5.

The TAG molecules may be thermally activated i.e., by heating thedispenser probe as described above (step 410, FIG. 4). The TAG moleculescould also be activated by heating the entire sample.

In the variant of FIG. 5, the probe is used to dispense PAG moleculeswhich are activated by irradiating the sample with light 60 of suitablewave-length (typically in the ultraviolet range), as depicted in step520.

In each of the above case, the film comprises polymer chains which areunstable (at least in part) under operating conditions. Be it obtainedby direct heating with the probe or induced protonation, the polymerchains are believed to unzip, at least partly, upon breaking onechemical bond of the chain. Thus, the polymer used is advantageouslychosen amongst a class of polymers which unzip upon breaking onechemical bond thereof.

The polymer whose chemical structure is depicted in FIG. 7 is one suchpolymer. As said, the polymer comprises approximately n=200 monomerunits equivalent to a molecular weight of 27 kDa. Clearly, a suitablepolymer film may essentially comprise polymer chains made of polymerssuch as depicted in FIG. 7. However, enhanced properties and operationease can be obtained with a polymer film involving additional compounds,as to be discussed now. To that aim, copolymers are synthesized, i.e.,they derive from two or more distinct monomers. One of the monomers is adialdehyde compound or the like, e.g., phthalaldehyde, such as to enableunzip reaction in fine. In addition, at least another monomer isinvolved that is chosen such as to confer specific properties to thefilm. This gives rise to two distinct embodiments. In the first one, thepolymer film comprises block-copolymer chains, while the secondembodiment uses copolymers of phthalaldehyde and functionalizablecompounds, such as benzaldehyde.

Block-Copolymer Embodiment

Here, at least some of the polymer chains (not necessary all of them)are block copolymers, i.e., involving two or more homopolymer blockunits (also called units). One of said blocks derives from dialdehydemonomers, which shall enable the unzip effect. For example, the polymerfilm is synthesized as a block-copolymer, wherein upward blocks (i.e.,blocks in contact with the air interface) corresponds to the polymer ofFIG. 7.

Thus, a core idea is to enhance patterning performance using polymerblock copolymers comprising the unzip polymer as one of the blocks andexploit properties such as ordering properties conferred by one or moreadditional blocks (call them “functional” block polymers). Inparticular, at least some of the polymer chains of the film may beordered and/or oriented by way of additional blocks that are more stablethan the unzip block (e.g. thermally more stable). The polymer chainsmay for instance be oriented perpendicularly to the plane of the polymerfilm (i.e., the mean chain orientation has a perpendicular component).The block copolymer chains may even form a structured pattern on thesurface of the film, such as a 2D lattice, whereby clean patterned filmcan be obtained.

Copolymers can for instance be deposited on a substrate 10, e.g., a Siwafer. The substrate can be overlaid by a neutral/compatibility layer12, if necessary, e.g., to attract the ordering block polymer to thesubstrate interface, see FIG. 6A or 6B. Highly ordered films of onemonolayer thickness can accordingly be formed, e.g., with unzip blocks32 facing upward as stretched strands. The defined thickness of thelayer 20 makes the patterning rather insensitive to the workingparameters. Ideally, absence of entanglement improves the aspect ratioand the minimum feature size of the written structures. In addition, thenonvolatile block at the substrate prevents the tip from touching thesubstrate directly, which incidentally can be detrimental to the tip.

In a first implementation (FIG. 6A), the chains 30 extend if at allpossible from the functional block 31 to the unzip block 32 (all chainsat the surface ideally have a path to the functional block interface).The blocks are preferably symmetric in length (i.e., they havesubstantially the same length; they can be regarded as Gaussian coils).Indeed, If the length of one of the blocks is less than half the lengthof the other block, the polymer tends to form cylinders or spheres ofthe shorter block in a matrix of the other block. At the surface such acylindrical phase would not lead to a uniform layer-like ordering asdepicted). As said, a neutral layer 12 may facilitates verticalorientation of the functional blocks. Then, the patterning process maysystematically penetrate to the functional block layer, as a result ofremoving the unzip polymer. Thus, removing an area of unzip polymer 32may result in a very clean surface, provided that functional blocks 31are suitably designed. As a consequence, the effective patterning depthobtained is made quite insensitive to forces. Also, a higher aspectratio of patterns can be achieved, in comparison to usual films.Therefore, a patterning of a chemical contrast (or “surface contrast”)can be achieved. A different chemistry is in fine exposed from thefunctional block layer: the chemical nature of the exposed surface canbe tailored by an according design of the first polymer block 31.

In a second implementation (FIG. 6B), copolymers are once more depositedto form ordered films of one monolayer thickness. Here the fraction ofthe unzip block is typically only ⅓rd of the total block molecularweight (or length). This leads to an arrangement of hexagonally orderedunzip cylinders (microdomains) 32 embedded in a matrix of the functionalpolymer 31. Using a neutral layer 12, at which neither of the blockspreferentially segregates. The cylinders 32 may be orientedperpendicular to the plane of the film, as shown in FIG. 6B. Here again,the unzip block can be ordered by way of the functional polymer block(the matrix). The ordering occurs because of the composition of theblock copolymer; in this case hexagonally ordered cylinders of theshorter block in a matrix of the longer block. The tip 50 can then beused to remove unzip blocks at desired prefix locations (such aslocation 25 on the film). Such an implementation combines advantagesprovided by the regularity of the block assembly 31, 32 together withlocally defined removal of unzip material. Otherwise put: clean “holes”of constant contrast are obtained at desired locations in the pattern,whereby information can reliably be encoded and read.

The pattern formed by block copolymer chains 30 can be tailoredaccording to various applications. This pattern can be ordered,repeated, etc., or not. In cases of repeating patterns (like in 2Dcrystals), the pattern as a whole may be regarded as a 2D lattice madeup of repeating basis patterns at lattice points. An elementary basispattern formed by block copolymer chains 30 on the top surface canitself be tailored, in some extent. Patterns available for blockcopolymers are spheres in a matrix, cylinders in a matrix or lamellae.FIG. 6B depicts cylinders; applications to nanowire gated transistors asdescribed below would however use lamellae, which are orientedperpendicular to the substrate plane. Said pattern can even change alongthe lattice. For instance, the above principle is advantageously appliedto multi-nanowire gated transistors, wherein wires can be removed withhot tip and the surviving pattern transferred into the substrate.Silicon bridges result between the drain and the source (not shown).

Chemical aspects are now discussed. As said, a preferred strategy is todesign one block that is thermally stable while the second block isunstable and decomposes on heating into volatile moieties. This enablesa solvent-free or dry patterning approach without the need to expose thesubstrate and resist to solvents, and the drawbacks associated with suchprocessing. The following discloses a route to block copolymers whereone block has a low ceiling temperature, i.e., one degradation event isamplified via an unzipping of the entire chain, while the second blockis thermally stable. We focus, but not restrict, this embodiment tocopolymers where one block is derived from poly(phthalaldehyde) thatundergoes rapid depolymerization at temperatures above ˜140° C. Thesecond block can be chosen amongst a variety of blocks, e.g., having afunctional group able to initiate a ring-closing polymerization ofphthalaldehyde. The preferred functional group is, but not restrictedto, an aliphatic alcohol. Polymerizations are accomplished below theceiling temperature of the Poly(phthalaldehyde) (−45° C.) and generallyat −78° C. The second block is preformed and can be prepared bycondensation, ring-opening, controlled radical, anionic, cationic orother synthetic methods provided an initiating group or groups can beplaced either at one or both chain-ends or along the polymer backbone.The preferred synthetic methods are controlled radical and anionictechniques owing to the wide range of monomeric substrates available andsynthetic methods available. In addition to an initiating group, otherfunctional groups are available that provide processability, solubility,wetting of the substrate, functional groups that can provide etchresistance, or post-dissolution.

Polymerizations are accomplished in solution (−78° C.) with an organiccatalysts such as N-heterocyclic carbenes or phospazene bases. Uponcompletion of the polymerization, while cold, the reaction is quenchedand the chains capped to prevent depolymerizaton while returning to roomtemperature. The polymer is isolated by precipitation and isolated byfiltration.

This can be exemplified through the synthesis of apolystyrene-phtalaldehyde block copolymer, schematically represented inFIG. 8. This synthesis is reported below.

To a 20 mL culture tube were charged phthalaldehyde (274 mg, 2.04 mmol),hydroxyl functionalized polystyrene (110 mg, M_(n)=9000 g/mol,PDI=1.05), and dry THF (3.0 mL) in a glove box. The tube was then sealedwith a rubber septum and cooled to −75° C. in a dry ice-acetone bath. A0.05 M THF solution of P2-t-Bu (0.1 mL) was added to the mixture througha needle to initiate the polymerization. After continuously stirring at−75° C. for 1 hour, trichloroacetyl isocyanate (TCAI) (˜0.1 mL) wasadded to quench the reaction and the mixture was kept stirring for atleast 2 hours under the chilled condition. Then the viscous solution wasallowed gently to warm up to room temperature and precipitated inmethanol twice. The precipitates were centrifuged and dried under vacuumto give poly(styrene-b-phthalaldehyde) as white solid (293 mg, 76%). 1HNMR (CDCl₃): □=7.75-6.19 (m, ˜1208H; ArH_(PPA), ArH_(PS), CH_(PPA)),3.33-3.16 (b, 2H; CH₂O), 2.29-1.16 (m, ˜85H; CH₂, CH_(PS)), 1.67-1.17(m, ˜179H; CH2_(PS)). GPC (THF, RI): M_(n)=11000 g/mol, PDI=1.51. Forcompleteness, GPC stands for “gel permeation chromatography”; M_(n) isthe number averaged molecular weight; PDI is for polydispersity index(how similar are the chains); the earlier numbers are positions of theresonances in the NMR spectrum.

Another example is the synthesis of a poly-L-lactide(PLLA)-phtalaldehyde block copolymer, see FIG. 9.

To a 20 mL culture tube, phthalaldehyde (268 mg, 1.99 mmol),poly-L-lactide (145 mg, M_(n)=21600 g/mol, PDI=1.11), and dry THF (3.0mL) were charged in a glove box. The tube was then sealed with a rubberseptum and cooled to −75° C. in a dry ice-acetone bath. A 0.05 M THFsolution of P2-t-Bu (0.1 mL) was added to the mixture through a needleto initiate the polymerization. After continuously stirring at −75° C.for 1 hour, TCAI (˜0.1 mL) was added to quench the reaction and themixture was kept stirring for at least 2 hours under the chilledcondition. Then the viscous solution was allowed gently to warm up toroom temperature and precipitated in methanol twice. The precipitateswere centrifuged and dried under vacuum to givepoly(L-lactide-b-phthalaldehyde) as white solid (206 mg, 50%). ¹H NMR(CDCl₃): □=8.27-7.82 (m, 9H; ArH_(pyrene)) 7.72-7.11 (m, ˜286H;ArH_(PPA)), 7.11-6.26 (m, ˜158H; CH_(PPA)), 5.25-5.05 (m, 160H;CH_(PLA)), 4.24-4.18 (m, 2H; CH₂O), 4.11-4.06 (m, 1H; CH_(junction)),3.40-3.35 (m, 2H; pyrene-CH₂), 1.96-1.79 (m, 4H; CH₂), 1.68-1.39 (m,˜549H; CH_(3 PLA)). GPC (THF, RI): M_(n)=10200 g/mol, PDI=1.64.

Copolymers of Phthalaldehyde and Benzaldehyde

While the previous embodiments have focused on block-copolymer chains,the polymer film can more generally exhibit chains of copolymers derivedfrom two or more monomers, where the structural units of the copolymersare not necessarily arranged in block. One of the monomers remains yet adialdehyde compound, e.g., a phthalaldehyde, such as to suitably enableunzip reaction. At least another monomer is involved that is chosen suchas to confer specific properties to the film.

In an embodiment, the polymer film comprises copolymers ofphthalaldehyde compounds and benzaldehyde compounds. The benzaldehyde isa commercially available compound and a variety of functionalbenzaldehydes are available that offer a facile means of introducingfunctional groups and enhancing polymer solubility/processability. Thisparticular benzaldehyde compound lowers the ceiling temperature, whichtherefore can be tuned by the molar fraction. For instance, aphthalaldehyde polymer such as that of FIG. 7 has a ceiling temperatureof ˜150 C. Using a film made up of single polymer chains ofphthalaldehyde typically requires tip heater temperatures>600° C., andheating times>10 μs for high-performance patterning (obviously, thisdepends on a number of experimental parameters). Now, high temperatureshave several drawbacks: the lever behavior of the AFM device (or thelike), calibration of force and temperature all are difficult toaccurately control. More importantly the scaling to smaller pulsedurations and higher patterning speeds is limited as even highertemperatures may result in destroying integrity of the lever. Therefore,it can be realized that a material with lower ceiling temperature (e.g.,of ˜100 to 120° C.) would be more convenient (as achieved with thebenzaldehyde copolymer). In addition, a pure phthalaldehyde platform maynot be versatile enough for some applications, it doesn't bear muchfunctionality other than unzipping and has marginal solubility thatrestrict the quality and thickness of the resist films.

To overcome such limitations, present inventors have developed anapproach to diversify the polymer backbone that provides the possibilityto tailor the decomposition temperature, improve solubility and henceprocessability. In addition, providing functional groups along thebackbone provide post-functionalization possibilities and versatility.

In the following, a family of monomers is discussed, namely,4-(Benzyloxy)benzaldehyde, 4-(Dimethylamino)benzaldehyde,4-(Hexyloxy)benzaldehyde, 4-[Bis-(2-chloroethyl)amino]benzaldehyde,3-(1,1,2,2-Tetrafluoroethoxy)benzaldehyde,4-(Diethoxymethyl)benzaldehyde, 4-(4-Morpholinyl)benzaldehyde,4-(1-Piperidinyl)benzaldehyde, 4-(Trifluoromethyl)benzaldehyde,4-(2-Pyridyl)benzaldehyde,4-(4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-Heptadecafluoroundecyloxy)benzaldehyde, 4-(4-Methylphenyl)benzaldehyde,4-(Methylthio)benzaldehyde, 2,4-Bis(trifluoromethyl)benzaldehyde,2-Fluoro-4-(trifluoromethyl)benzaldehyde,3,5-Bis(trifluoromethyl)benzaldehyde, 4-(Boc-amino)benzaldehyde,4-[(2-Cyanoethyl)methylamino]benzaldehyde,4-[(tert-Butyldimethylsilyl)oxy]benzaldehyde, etc.

Such monomers can be co-polymerized with the core polymer via anorganocatalytic approach to generate polymers of predictable molecularweights and narrow polydispersities, according to embodiments. To thataim, the chemistry of organocatalysis as applied to polymer chemistry isextended to the copolymerization of phthalaldehyde with benzaldehydes.The core phthalaldehyde monomer is difficult to functionalize and thereare no commercial variant to this structure, to the knowledge of presentInventors. In contrast, benzaldehyde and functionalized benzaldehydesare pervasive and commercially available.

Next, the desired copolymerization can be demonstrated. These polymersshow different decomposition temperatures, depending on the nature ofthe substituent(s), i.e., electron donating/withdrawing, solubility andoffer the possibility of post modification. The versatility of thisapproach and a small sample of monomers that can be employed are forinstance shown in FIG. 10.

An example of a suited copolymerization protocol follows, see also FIG.11. In a nitrogen filled glovebox a test tube was charged withphthalaldehyde (0.200 g, 1.49 mmol), benzaldehyde (0.0200 g, 0.188mmol), THF (1.50 g), benzyl alcohol (0.8 {circle around (3)}L, 0.00745mmol) and a stir bar. In a separate vial, P₂-tBu Phosphazene base(0.00280 g, 0.00762 mmol) was dissolved in THF (0.500 g). Both solutionswere removed from the glove box and cooled to ˜78° C. Upon temperatureequilibration, the P₂-tBu Phosphazene base solution was syringeddirectly into the monomer mixture. The reaction temperature wasconstantly maintained at −78° C. for one hour at which pointtrichloroacetyl isocyante (100.0 mL, 0.839 mmol) was injected to quenchthe polymerization. The reaction mixture was then left in the cooling tobath to slowly warm to ambient temperature over a period of severalhours. The polymer solution was then added to stirred iPrOH (20 mL)causing the polymer to precipitate. The white powder was collected viavacuum filtration yielding 0.193 g (88%). M_(n)=13.7 kDa, M_(w)=23.8kDa, PDI=1.74. TGA/DSC: T_(d)=119° C., T_(m)=119° C. NMR: 7.15-7.80(ar-H), 6.33-7.15 (ar-H).

Finally, the properties of copolymer materials (such as described above)as a lithographic medium was demonstrated. For example, a 50 nm thinfilm of copolymer was spun-cast on a silicon substrate and patternedusing heated probes, as described in reference to FIG. 1. The probeswere electrostatically actuated and heated with an integrated heaterdirectly attached to the tip, as known per se. ‘Pixels’ were written bysimultaneously applying a force and a heat pulse to the cantilever for15 μs. A 500° C. tip-heater temperature was used, corresponding toelevating the polymer temperature to 230-270° C. As a result of thethermal activation, unzipping effects were observed. Note that thecomplete chain of the copolymer of FIG. 11 unzips. The disintegration ofthe unzip molecule into both monomer constituents. The monomer units atstake are highly volatile because of their low molecular weight (e.g.,134 Da and 106 Da). Thus, a fixed amount of material on the order of thevolume occupied by one unzip polymer block removed whenever a bond isthermally broken. An efficient material removal was accordingly obtainedas spontaneous depolymerization is faster than the mean initiation rateof bond-breaking governed by thermodynamic statistics.

A confirming image of the sample surface can then be obtained by readingpatterns on the obtained surface. This is typically achieved by usingthe same probe as for patterning. As explained earlier, theprobe-surface interaction is recorded as a function of position andimages are produced as a two-dimensional grid of data points.

In conclusion, the experimental results , together with methods andprinciple discussed above demonstrate the possibility for patterning andsubsequently reading polymer films with polymer chains of copolymersderived from two or more monomers (one of them being a dialdehydecompound), whereby polymer chains are able to unzip upon suitedstimulation. Such methods can be exploited to pattern large areas of apolymeric film with high throughput and resolution, demonstrating alow-cost, table top, nanoscale patterning method.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation to theteachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.For example, the present invention may be contemplated for variousapplications. While embodiments described above merely focus on uses forlithography (and data storage, implicitly), the skilled person mayappreciate potential applications to pattern transfer of patternedregions into silicon.

1. A method of reading nano-scale dimensioned patterns in a polymer filmof a material, comprising: providing a material comprising a polymerfilm, the film comprising polymer chains which can be unzipped uponstimulation; and nano-scale dimensioned patterns in the film, whereinthe polymer chains comprise copolymers derived from two or moremonomers, one of the monomers being a dialdehyde compound, and whereinthe nano-scale dimensioned patterns are obtained according to a methodcomprising stimulating the film with a nano-scale dimensioned probe forselectively triggering an unzipping reaction of the polymer chains ofthe film to provide the nano-scale dimensioned patterns; and reading thepatterns.
 2. The method of claim 1, wherein the polymer film providedcomprises polymer chains for which an energetic or chemical modificationevent triggers the unzipping reaction and wherein patterning includesstimulating the film such that an energetic or chemical modificationevent occurs in at least one polymer chain.
 3. The method of claim 1,wherein the polymer film provided comprises polymer chains which areable to unzip upon breaking one chemical bond thereof and whereinpatterning includes stimulating the film to break one bond of at leastone polymer chain.
 4. The method of claim 1, wherein patterning includeshaving the probe provide an energy to the film to activate a chemicalreaction involving a reactant in proximity with polymer chains, thechemical reaction allowing in turn for unzipping at least one polymerchain.
 5. The method of claim 4, wherein the reactant is anacid-generator.
 6. The method of claim 5, wherein the polymer film isprovided with the acid-generator comprised therein, the acid-generatorbeing activated during patterning.
 7. The method of claim 5, wherein theacid-generator is dispensed by the probe during patterning.
 8. Themethod of claim 5, wherein the acid-generator is athermal-acid-generator, the thermal-acid-generator activated by theprobe, heated during patterning.
 9. The method of claim 5, wherein theacid-generator is a photo-acid-generator, the photo-acid-generatoractivated by light during patterning.
 10. The method of claim 1, whereinsaid one of the monomers is a phthalaldehyde compound.
 11. The method ofclaim 10, wherein polymer chains of the polymer film provided comprisescopolymers of phthalaldehyde compounds and benzaldehyde compounds. 12.The method of claim 11, wherein at least some of the benzaldehydecompounds in the polymer chains of the polymer film provided arefunctionalized benzaldehyde compounds.
 13. The method of claim 1,wherein the polymer chains of the polymer film provided globally derivefrom at least two compounds, one of the compounds being the dialdehydecompound, and wherein at least some of the polymer chains of the polymerfilm provided comprise block copolymers of two or more homopolymerunits, one of the homopolymer units deriving from the dialdehydecompound, whereby said at least some of the polymer chains are able tounzip upon stimulation.
 14. The method of claim 13, wherein said atleast some of the polymer chains of the polymer film provided areordered by way of another one of the homopolymer units, substantiallymore stable than said one of the homopolymer units upon stimulation. 15.The method of claim 14, wherein the polymer chains in the polymer filmprovided have an average orientation with a non-zero componentperpendicular to a plane of the polymer film.
 16. The method of claim15, wherein the polymer chains in the polymer film provided are furtherordered such that said at least some of the polymer chains that compriseblock copolymers form a structured pattern in the plane of the polymerfilm.
 17. The method of claim 15, wherein the polymer chains in thepolymer film provided are further ordered such that said at least someof the polymer chains that comprise block copolymers form atwo-dimensional lattice in the plane of the polymer film.
 18. The methodof claim of claim 13, wherein said one of the homopolymer units derivesfrom a phthalaldehyde compound, whereas another one of the homopolymerunits derives from a compound comprising a functional group capable ofinitiating a ring-closing polymerization of phthalaldehyde.